Hierarchical mode I and mode II interlaminar toughening of Z-pinned composites using 1D and 2D carbon nanofillers

Abstract Through-thickness reinforcements using z-pins is a highly effective method for increasing the delamination resistance of fibre-polymer laminates. Here we report a hierarchical approach of incoporating carbon nanofillers and z-pins to further improve delamination toughness. The nanofillers include one-dimensional (1D) carbon nanofillers (e.g. carbon nanotubes, carbon nanofibres) or two-dimensional (2D) nanofillers (i.e. graphene nanoplatelets). Results of the interlaminar fracture toughness reveal that 1D nanofillers induce synergistic (i.e. greater-than-additive) improvements to both modes I and II delamination resistance of z-pinned laminates, whereas the 2D nanofiller show virtually no effect. Observations of the z-pin pull-out surfaces and the fracture surfaces reveal the main mechanisms why 1D nanofillers create a synergistic toughening effect, but not the 2D nanofillers.